The processing of reaction resins based on methyl (meth)acrylate floor coatings is normally associated with a strong offensive odor and significant air born toxicity. The low flash point and high volatility of methyl (meth)acrylate monomer also add costs when it is handled during manufacturing, packaging, transportation and application.
Polymerization of MMA monomer in the mixed solution of non-reactive bead polymer of methacrylates with tertiary amine or similar derivatives as amine synergist, benzoyl peroxide as initiator and wax as an oxygen barrier to form a Methacrylate floor coating resin has been broadly practiced in flooring and construction industry. The advantage of this technology is that it can be completely cured in one hour while the other coatings will need much longer time, typically at least six hours or more. Cured MMA film also exhibits excellent chemical resistance and abrasion resistance. However, many such coatings have issues with odor, volatility, toxicity and flammability.
Low-odor (meth)acrylate coating systems are known, consisting largely of slightly higher MW monomers as incorporation of larger compounds such as higher oligomers and polymers often complicate application of the coating, especially in low solvent or solvent free coatings. Controlling the odor, in many instances, also somewhat lowers the toxicity as many of the volatiles responsible for the odor also contribute to the toxicity. However, to achieve 100% cure while maintaining the good balance between the work time and curing time is difficult and health risks often remain a concern even for these low odor systems. The need for a low-odor, cold-curing (meth)acrylate reaction resin for a floor coating that has especially low health risks during application remains.
Historically, coating materials comprising thermoplastic and thermosetting polymers were applied from solvents that were subsequently removed by evaporation. However, changing safety, health and environment legislation have restricted solvent emissions and solvent-free coating materials and lacquers have become known.
UV curable coatings offer very fast compared to other methods, such as moisture curing or thermal curing. Typical UV lacquers or varnishes are applied at room temperature and often consist of epoxy acrylate, polyester acrylate or urethane acrylate oligomers combined with acrylate functional monomers in the presence of a photoinitiator. Under suitable UV wavelengths, the photoinitiators produce free radicals which polymerize the acrylate functional groups to produce a cross-linked network. The relatively high concentrations of low viscosity reactive monomers often employed to reduce the viscosity of the coating composition in order to get good flow and leveling at room temperature can penetrate into porous substrates such as wood and become too deep to be cured by UV radiation. Uncured monomer in the pores of substrates can give safety, health and environmental problems, e.g., when the materials are cut or sanded.
The use of a solvent-free reactive hot melt layer based on polyurethane and hardened by atmospheric humidity has been suggested. While this method is advantageous in that desired layer thicknesses can be applied in a single operation, curing takes at least several days to occur because it depends on moisture and the coated part cannot be processed or packaged rapidly.
Hot melt compositions that can be cured through both radiation and moisture or by applying a UV curable lacquer on top of the moisture curable hot melt are known wherein the coating is partially cured by UV radiation, typically the top layer of portion of the coating, but full cure of the full coating may still take several days. Also, required heating the hot melt composition prior to application limits thermal stability resulting in moisture from the atmosphere penetrating the composition and reacting with the isocyanate groups. This leads to an increase in molecular weight while on the roller and application problems, e.g., stringing or filament formation that can produce fouling of substrates/application equipment.
US 2009/0082485 discloses radiation curable hot melt coating compositions and articles comprising them. Typical compositions comprise a polymer component with number average molecular weight (Mn)>2,000 g per mole comprising polyurethane and/or poly(meth)acrylate segments and at least one functional group polymerisable under UV radiation; an oligomeric component with Mn=500 to 5,000 g per mole and at least two functional groups polymerisable under UV radiation; at least one photoinitiator; and optionally either in place of or in addition to the oligomeric component, a monomer component with Mn=100 to 1,000 g per mole and at least one functional group polymerisable under UV radiation.
U.S. Pat. No. 7,049,355 discloses a low odor thermal curable floor coating formulation comprising low volatile methacrylate monomers, a non-reactive bead polymer, a paraffin and/or wax, and a redox system, containing an accelerator and a peroxide catalyst or initiator in an amount adequate for cold-curing the methacrylate monomers.
Despite advancements made, compositions with lower odor, less toxicity, decreased flammability, faster curing and better balance between working time and curing time are needed. These improvements can be found in the coating compositions of the present invention along with the production of coating films with better chemical and physical properties.